This invention relates to an alarm system, and more particularly to a low tire pressure alarm system.
It is well known in the art to mount on or about a valve stem of a single pneumatic tire an assembly of a low tire pressure detector and a radio transmitting device. Upon detection of a pressure drop below a predetermined level by the low tire pressure detector, the radio transmitter transmits a radio frequency alarm signal to a receiving antenna of a receiving set, usually mounted in the cab of a vehicle to actuate an alarm to apprise the driver of the corresponding low pressure in the monitored tire.
Another example of a similar type of low tire pressure alarm system in which the radio transmitter and antenna are mounted in a shielded hub casing is disclosed in the prior Fujikawa et al U.S. Pat. No. 3,950,726, issued Apr. 13, 1976. In the Fujikawa et al patent, the tire pressure detector is still located, either adjacent to or connected to the air valve stem, at a radial distance from the rotary axis from the vehicle wheel.
In the Shumway U.S. Pat. No. 4,048,614, issued Sept. 13, 1977, a miniature tire pressure detector and radio transmitter are attached directly to the air valve stem, and located in the air space within the monitored tire.
All of the above low tire pressure alarm systems are designed for single tires on single vehicle wheels, only. Moreover, all of the above detector devices are located radially outward of the rotary axis of the single wheel, and thereby become subjected to substantial centrifugal force, particularly if the vehicles are driven at high speed.